FIGS. 1 and 2 show examples of previous attempts at light bar wiring technologies 10 that include bulky, multi-conductor wiring harnesses 12 for carrying illumination-control signals from a set of discrete inputs 16 to each corresponding light head 20 in a light bar 26 (FIG. 2). Each light head 20 has at least one separate wire connection 30 that is assembled based on a predetermined wire-color combination. Additional wires 34 (FIG. 2) to each light head 20 may provide different illumination-control signals, some of which are applicable to only a subset of light heads or a subset of lighting components available within a light head. For example, multicolor-emitting modules typically expect several dedicated wires for each light-emitting diode (LED) color present in a light head. Thus, the wiring scheme becomes inherently complicated, as shown in FIG. 2. The numerous wires and light heads in light bar 26 tend to increase the likelihood of various installation errors. Mismatched wire colors and location-installation errors, e.g., due to assembly errors, compromise product functionality. The complex wiring scheme results in increased assembly and test time, both of which increase production and support costs attributable to previous light bar wiring technologies 10. Given the sheer number of LED module types and combinations, electronic quality control is fraught with practical challenges.
Rudimentary attempts to mitigate the aforementioned deficiencies have included serial bus technologies 40 of FIGS. 3 and 4, which are limited to an external-facing serial bus interface 42 provided as a substitute for discrete inputs 16 (described previously). A serial bus 44 facilitates communication of serial data received at a light bar 46 (FIG. 4). The data are then converted by an integrated circuit (IC) 50 (e.g., a microcontroller) into signals carried by discrete wires 30 to light heads 20, as described previously. Serial bus technologies 40, therefore, rely on circuitry 50 to interpret serial messages and convert them into illumination-control signals carried through discrete wires 30 housed inside light bar 46. For light bar manufacturers intending to implement serial connectivity in their light bar products, these previous attempts fall short of providing individual serial connections to each light head within a light bar.
FIG. 5 shows one example of an implementation of serial bus 44 in the form of a linear Controller Area Network (CAN) serial data bus 54. The CAN serial data bus (CAN bus, or simply CAN) standard describes a message-based protocol that was originally designed for multiplexing electrical wiring within automobiles, but it has uses in many other contexts. For example, CAN is commonly employed in the automotive industry to facilitate communications that need not include a host for controlling communications between various microcontrollers and so-called Electronic Control Units (ECUs, more generally known as CAN nodes 62, or simply nodes). In other words, CAN is a multi-master serial bus standard for connecting two or more nodes forming a serial communications network.
Robert Bosch GmbH published several versions of the CAN specification, the latest of which is CAN 2.0 published in 1991. This specification has two parts: part A describes a so-called standard format for a CAN message having an 11-bit identifier field, and part B describes the so-called extended format having a 29-bit identifier. A CAN device employing standard format 11-bit identifiers is commonly called a CAN 2.0A (compliant) device, whereas a CAN device employing extended format 29-bit identifiers is commonly called a CAN 2.0B device. Furthermore, in 1993 the International Organization for Standardization (ISO) released the CAN standard ISO 11898 that developed into the following three parts: ISO 11898-1, which specifies the data link layer; ISO 11898-2, which specifies the CAN physical layer for high-speed CAN implementations; and ISO 11898-3, which specifies the CAN physical layer for low-speed, fault-tolerant CAN implementations. FIG. 5 shows an example implementation of the high-speed specification that describes linear CAN bus 54 including three CAN nodes 62 connected to one another through two wires 82 terminated at each end with 120 ohm (Ω) resistors 84. Wires 82 are 120 nominal twisted pair, according to one embodiment.